JP3304724B2 - Dual mode filter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dual mode filter used in a high frequency region such as a UHF band, a microwave band, and a millimeter wave band.

[0002]

2. Description of the Related Art Radio equipment using high frequency is required to be small, lightweight and low-cost. For this purpose, there is a strong demand for downsizing of filtering devices such as an antenna duplexer and an interstage filter which occupy a particularly large mounting area among wireless devices.

[0003] A conventional filter will be described below.
Here, as an example, a two-stage side-coupled high-frequency filter using a microstrip line will be described.

FIG. 14 is a configuration diagram of a side-coupling type high frequency filter. In FIG. 14, reference numerals 201 to 202 denote a half-wavelength strip line resonator having a parallel coupling portion,
Numerals 03 to 204 denote input / output coupling circuits for connecting the stripline resonator to an external circuit. With the above configuration, this filter operates as a band-pass filter at high frequencies.

[0005]

However, since the above-mentioned conventional filter uses a half-wavelength resonator having an open end, radiation loss is larger than that of a one-wavelength ring resonator. Further, when narrow-band characteristics are obtained by the above-described conventional filter configuration, the distance between two resonators forming interstage coupling must be greatly increased. Therefore, the whole shape becomes large. Further, since weak interstage coupling is realized by increasing the interval between parallel coupling lines, the coupling is easily affected by the external environment, and the stability of the coupling degree decreases.
Furthermore, if a quarter-wavelength resonator is used for downsizing, the whole can be downsized. However, a ground plane treated with through holes or the like is required on the resonator forming surface.

As described above, when a narrow band filter is realized by the conventional configuration, there is a problem that the shape becomes large and the characteristics are likely to be unstable.

The present invention solves the above-mentioned conventional problems. In the high-frequency region, a ground plane is not required on a resonator forming surface, and it has a small size and is stable to an external environment. It is intended to provide an effective filter for.

[0008]

In order to achieve the above object, a dual mode filter according to the present invention comprises a ring resonator having a high-frequency transmission line formed in a ring shape, and a ring resonator connecting the ring resonator to an external circuit. A first input / output coupling circuit comprising: first and second input / output coupling circuits; and a discontinuous portion having a function of causing electromagnetic field discontinuity with respect to a resonance mode excited by the ring resonator. Is connected at a first coupling point provided at an arbitrary position on the ring resonator, and the second input / output coupling circuit is a quarter of the length of the ring resonator from the first coupling point. Are connected at a second connection point provided at a distance from the first connection point, and are located between the first and second connection points and have the center of a shorter one of two lines forming the ring resonator. Is the first point of symmetry, the first point of symmetry is By providing a part, it constitutes a high-frequency filter having stable characteristics in small, compact filter can be realized as compared with the conventional filter. In addition, since the inter-stage coupling is realized by the discontinuous portion provided in the ring resonator, a filter having stable characteristics with respect to the external environment can be realized.

[0009]

[0010]

[0011]

[0012]

[0013]

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 or 2 of the present invention comprises a parallel coupling line portion in which a part of a line forming a ring resonator is bent 180 degrees at a first symmetry point and parallel coupled. A discontinuous portion is formed by the parallel coupling line portion, and a reflected wave is generated by parallel coupling between the lines, and the first and second coupling points are coupled. Thus, there is an effect that the two-stage filter is constituted by one resonator.

According to a third aspect of the present invention, there is provided a filter according to the first aspect, wherein a line is bent inside the ring resonator to form a discontinuous portion. Forming a parallel coupling line inside a ring resonator that easily becomes a dead space has the effect of configuring a smaller filter.

According to a fourth or fifth aspect of the present invention, two points separated by the same length from the first symmetry point are connected by a lumped constant element such as a capacitor or an inductor, or electromagnetically coupled by a parallel coupling line. A filter comprising a continuous portion, wherein the first and second input / output coupling circuits and the lumped constant element are provided at positions that are topologically symmetric with respect to the first symmetry point. Accordingly, the first and second coupling points are coupled through the lumped constant element, and the two-stage filter can be constituted by one resonator.

[0017]

[0018]

An embodiment of the present invention will be described below with reference to FIGS. (Embodiment 1) FIG. 1 is a plan view of a dual mode filter according to a first embodiment of the present invention.

In FIG. 1, 101 is a ring resonator, 1
02 to 103 are input / output coupling circuits connected to external circuits,
04 is an open-end stub constituting a discontinuous portion, 105 to 1
Reference numeral 06 denotes a connection point at which the input / output coupling circuits 102 and 103 are connected to the ring resonator 101, and reference numeral 107 denotes a symmetric point at the center of the shorter one of the lines connecting the connection points 105 and 106. . Coupling points 105 and 106 are separated from each other by a quarter of the length of ring resonator 104, and point of symmetry 107 is separated from coupling points 105 and 106 by one-eighth of the length of ring resonator 104. The location is located.

The operation of the dual mode filter configured as described above will be qualitatively described below with reference to FIG. 1 using the concept of a traveling wave. The traveling wave propagated from the input / output coupling circuit 102 is electrically coupled to the ring resonator 101 and generates a strong electric field near the coupling point 105. This electric field propagates in the clockwise and counterclockwise directions as a traveling wave. First, consider a clockwise traveling wave.

The traveling wave reaches the output-side connection point 106 after undergoing a 270 ° phase change, but does not couple to the output connection point 106 because the electric field is minimized here. When the position is further advanced by 45 °, the position of the symmetry point 107 is reached. Here, since a discontinuous portion exists in the line due to the open-end stub 104, a part thereof becomes a reflected wave, and the rest propagates to the coupling point 105 on the input side and is coupled to the input terminal via the input / output coupling circuit 102. The reflected wave at the point of symmetry 107 recedes by 45 ° and reaches the output side coupling point 106. However, since the phase difference is 360 ° round trip, the electric field becomes maximum here, electric field coupling occurs, and the electric field coupling via the input / output coupling circuit 103 Thus, the traveling wave propagates to the output end.

Similarly, as for the traveling wave in the counterclockwise direction, only the reflected wave from the open-end stub 104 appears at the output end. Since the magnitude of the reflection is remarkable when the discontinuous portion is large, FIG.
In the case of, the size of the traveling wave propagating by the length of the open stub can be controlled. When this operation is viewed as a resonator, there are two orthogonal modes in the ring resonator 101,
This means that the degree of coupling between the two resonance modes can be controlled by the structure of the open-end stub.

That is, it can be considered that the device operates as a dual mode filter and one resonator has a function corresponding to a two-stage filter, and it can be said that the configuration contributes to downsizing.

In the dual mode filter of this configuration, the inter-stage coupling can be controlled by the structure of the open end stub which is a discontinuous portion. As compared with the configuration for obtaining the coupling, a stable characteristic is obtained that is less affected by the external environment.

FIGS. 2 (a) and 2 (b) show configurations using a short-circuited stub and a notch at the discontinuous portion, respectively.
If a ground plane can be mounted on the resonator forming surface, it is possible to form a discontinuous portion by a short-circuit stub at the tip. FIG.
The dual mode filter configured as described above operates as a dual mode filter similarly to the configuration using the open-end stub of FIG.

As described above, according to the present embodiment, 1
Since a two-stage filter can be formed by one resonator, a filter having a small size in a high frequency region and having stable characteristics with respect to an external environment can be formed. (Embodiment 2) FIG. 3 is a plan view of a dual mode filter according to a second embodiment of the present invention.

In FIG. 3, components denoted by the same reference numerals as those in FIG. 1 have the same functions as those in FIG. 3 differs from FIG. 1 in that an open-end stub 104 constituting a discontinuous portion is provided inside a ring resonator 101.

The operation of the dual mode filter configured as described above will be described below. The basic operation is the same as in the first embodiment. The dual mode filter of the present embodiment is configured by mounting an open-end stub inside a ring resonator that is a dead space,
The filter can be configured with a smaller occupied area than in the first embodiment.

As described above, according to the present embodiment, by providing the discontinuous portion inside the ring resonator, it is possible to configure a dual mode filter with a small area.

FIG. 3 shows an example in which an open-end stub is used as a discontinuous portion. However, if a ground plane can be formed by using a through hole or the like inside the ring resonator, the short-circuited stub is connected to the ring resonator. The same effect can be obtained by providing it inside. (Embodiment 3) FIG. 4 is a plan view of a dual mode filter according to a third embodiment of the present invention.

In FIG. 4, components denoted by the same reference numerals as those in FIG. 1 have the same functions as those in FIG. 4 is different from FIG. 1 in that the discontinuous portion is constituted by a discontinuous line 108 having a width different from that of the ring resonator 101, and the discontinuous line 108 is set in a range equidistant from the symmetry point 107 to both sides. This is the point provided.

The operation of the dual mode filter configured as described above will be described below. The basic operation is the same as in the first embodiment. In the present embodiment, the reflected wave with respect to the traveling wave is realized by changing the characteristic impedance. The larger the difference between the characteristic impedances, the larger the amount of reflection at the discontinuous portion. Therefore, the coupling between the two orthogonal modes becomes stronger, and a filter having a wider pass band is configured. The degree of coupling can also be controlled by changing the length of the discontinuous line.

As described above, according to the present embodiment, a two-stage filter can be formed with one resonator by forming the discontinuous portion with a line having a width different from that of the ring resonator. Thus, a filter having a small size and stable characteristics with respect to an external environment can be formed.

Although FIG. 4 shows an example in which the discontinuous line is made thicker than the ring resonator line and the characteristic impedance of the discontinuous line is lowered, the width of the discontinuous line is made narrower. Even if the characteristic impedance is increased, a reflected wave is generated with respect to the traveling wave, and the same effect can be obtained. FIG. 4 shows an example in which the characteristic impedance is changed stepwise, but it goes without saying that the same effect can be obtained even if the changed portion is tapered. (Embodiment 4) FIG. 5 is a perspective view of a dual mode filter according to a fourth embodiment of the present invention.

In FIG. 5, the same reference numerals as in FIG. 1 have the same functions as those in FIG. 5 is different from FIG. 1 in that the discontinuous portion is constituted by a discontinuous portion line 108A mounted on a substrate thickness different from that of the ring resonator 101, and the substrate thickness is continuously changed.

The operation of the dual mode filter configured as described above will be described below. The basic operation is the same as in the first embodiment. In the present embodiment, the characteristic impedance of the discontinuous line is made different from the characteristic impedance of the ring resonator by changing the thickness of the dielectric substrate 109 on which the discontinuous line 108A is mounted, and a reflected wave is generated. By doing so, the two orthogonal modes are coupled. In this embodiment, the degree of coupling can be controlled by the difference in substrate thickness.

As described above, according to the present embodiment, a two-stage filter can be constituted by one resonator by mounting the discontinuous portion on a substrate having a thickness different from that of the ring resonator. A filter having a small size and stable characteristics with respect to an external environment can be formed.

FIG. 5 shows an example in which the substrate thickness of the discontinuous line is made thicker than that of the ring resonator line to increase the characteristic impedance of the discontinuous line. Even if the characteristic impedance is lowered by thinning
A reflected wave is generated with respect to the traveling wave, and a similar effect is obtained.
Although FIG. 5 shows an example in which the characteristic impedance is continuously changed, it is needless to say that the same effect can be obtained even if the changed portion is stepped. (Embodiment 5) FIG. 6 is a plan view of a dual mode filter according to a fifth embodiment of the present invention.

In FIG. 6, components denoted by the same reference numerals as those in FIG. 1 have the same functions as those in FIG. 6 is different from that of FIG.
This is a point formed by a parallel coupling line portion 110 which is bent at every time and a part of the ring resonator 101 is coupled in parallel.

The operation of the dual mode filter configured as described above will be described below. The basic operation is the same as in the first embodiment. In the present embodiment, a reflected wave is generated by the parallel coupling line section 110, and two orthogonal modes are coupled. In the present embodiment, the degree of coupling between the orthogonal modes can be controlled by the coupling length, degree of coupling, and characteristic impedance of the parallel coupling line section 110.
By adjusting the coupling length so that the degree of coupling of the parallel coupling line portion becomes strong, it is possible to obtain stable characteristics with respect to the external environment.

FIG. 7 shows a configuration in which the parallel coupling line section 110A is formed of a line having a length of one-fourth or more of the ring resonator 101, and coupling points 105 to 106 are provided inside the parallel coupling line section. ing. The configuration of FIG. 7 operates similarly to FIG.
The dual mode filter of the present embodiment can be configured.

As described above, according to the present embodiment, the discontinuous portion is constituted by the parallel coupling line portion in which a part of the ring resonator is parallel-coupled, so that one resonator has two stages of filters. , A filter having a small size in a high frequency region and having stable characteristics with respect to an external environment can be formed.

Although FIGS. 6 and 7 show an example in which the parallel coupling line portion is arranged outside the ring resonator, the occupation area can be further reduced by disposing the parallel coupling line portion in the ring. It is possible. (Embodiment 6) FIG. 8 is a plan view of a dual mode filter according to a sixth embodiment of the present invention.

In FIG. 8, components denoted by the same reference numerals as those in FIG. 1 have the same functions as those in FIG. 8 differs from FIG. 1 in that a discontinuous portion is formed by a lumped constant inductor 111 connecting two points equidistant from the coupling points 105 and 106 on the ring resonator line toward the symmetry point 107. It is.

The operation of the dual mode filter configured as described above will be described below. The basic operation is the same as in the first embodiment. In the present embodiment, by providing a propagation path of a wave excited on the resonator other than on the ring resonator by the lumped constant inductor 111,
Two orthogonal modes are combined. The position at which the lumped-parameter inductor 111 is connected to the ring resonator 101 is determined at the point of symmetry 10 on the ring resonator line from the coupling points 105 and 106.
It is equidistant towards 7 and can be installed in any location that is entirely topologically symmetric. In the present embodiment, the degree of coupling between the orthogonal modes is determined by the lumped constant inductor 1
11 and the connection position of the lumped constant inductor.

FIG. 9 shows an example in which the lumped-constant inductor is replaced with a parallel coupling line formed by a line forming the ring resonator 101. 9 operates in the same manner as in FIG. 8, and the dual mode filter of the present embodiment can be configured. In FIG. 9, the degree of coupling between orthogonal modes can be controlled by the coupling length, degree of coupling, and characteristic impedance of the part to be parallel-coupled.

As described above, according to the present embodiment, the point of symmetry 1 on the ring resonator line is established from the coupling points 105 and 106.
By using a lumped-parameter inductor connecting two points equidistant toward 07, or by connecting two places equidistant from the symmetry point 107 in parallel to form a discontinuous portion, two resonators can be realized by one resonator. Since a filter at the stage can be configured, a filter having a small size in a high frequency region and having stable characteristics against an external environment can be configured.

It is to be noted that a similar dual mode filter can be formed by replacing the lumped constant inductor of FIG. 8 with another element such as a lumped constant capacitance or a gap capacitor. (Embodiment 7) FIG. 10 is a plan view of a dual mode filter according to a seventh embodiment of the present invention.

In FIG. 10, the components denoted by the same reference numerals as those in FIG. 1 have the same functions as those in FIG. 10 differs from FIG. 1 in that the open-end stubs 112 to 115 are provided at connection points 105 to 106 and at a point separated from the connection point by a quarter of the length of the ring resonator 101.

The operation of the dual mode filter configured as described above will be described below. The basic operation is the same as in the first embodiment. In the present embodiment, open-end stubs 112 to 115 are provided at points where the electric field becomes maximum or zero in the ring resonator so that the center frequency of the dual mode filter can be adjusted. The center frequency can be increased by trimming the four open stubs in the same manner. Therefore, if the center frequency of the filter is designed to be slightly lower in advance, it becomes possible to adjust the center frequency to a desired center frequency by shaving the end of the stub.

As described above, according to the present embodiment, trimming adjustment of the center frequency can be performed by the stub having an open end, and a filter having a small size and stable characteristics with respect to an external environment can be configured. (Eighth Embodiment) FIG. 11 is a plan view of a dual mode filter according to an eighth embodiment of the present invention.

In FIG. 11, components denoted by the same reference numerals as those in FIG. 1 have the same functions as those in FIG. 11 differs from FIG. 1 in that a plurality of dual mode filters shown in FIG. 1 are connected via interstage coupling circuits 116 to 118.

The operation of the dual mode filter configured as described above will be described below. The basic operation is the same as in the first embodiment. In this embodiment, since the filter having two or more stages is configured, the dual mode filter shown in the first embodiment is connected to the interstage coupling circuits 116 to 11.
8 are connected in cascade, and a filter can be realized with a ring resonator having half the number of stages, so that a small filter can be realized. The degree of interstage coupling of the multistage filter can be adjusted by an interstage coupling circuit and a discontinuous portion provided in the ring resonator.

As described above, according to the present embodiment, a multistage filter can be realized with half the number of resonators by connecting a plurality of ring resonators each having a discontinuous portion in an interstage coupling circuit. Therefore, a filter having a small size and stable characteristics with respect to an external environment can be formed.

Although FIG. 11 shows an example in which a plurality of dual mode filters of the present invention in which the discontinuous portion is formed by a stub having an open end are connected, a dual mode filter having another configuration shown in the seventh embodiment is used. It goes without saying that the multi-stage filter of the present embodiment can be configured even if it is used.

Although the lumped-constant capacitance is used for the input / output coupling circuit in the embodiments except the fifth embodiment, it goes without saying that the same effect can be obtained by using another coupling circuit such as a gap capacitor. Further, in all the embodiments, the ring resonator 101 is circular. However, as long as the lines forming the ring resonator are connected in a topological ring shape, the ring resonator 101 does not have to be circular, and may be adjusted to the mounting space. Needless to say, it can be deformed.

[0058]

【Example】

(Embodiment 1) Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. FIG. 12 is a configuration diagram of a dual mode filter according to the first embodiment of the present invention, and FIG. 13 is a diagram illustrating characteristics of the dual mode filter having the configuration of FIG.

In FIG. 12, C1 and C2 denote element values of a lumped constant capacitance serving as an input / output coupling circuit;
Is the electrical length of the open-end stub at the frequency f. The electrical length of the ring resonator at the frequency f is shown inside the ring resonator. Z1 and Z2 are 50Ω, f is 1 GHz
FIG. 13 shows the characteristics when the stub electric length E1 is 10 ° and 30 °.

The characteristic A in FIG. 13A shows that the stub length is 10 °.
And the transmission and reflection characteristics when the input / output coupling capacitance (C1 to C2) is 0.8 pF.

In the characteristic B of FIG. 13B, the stub length is 30 °.
And the transmission and reflection characteristics when the input / output coupling capacitance (C1 and C2) is 1.6 pF.

When the stub length is increased, the coupling between the orthogonal modes becomes stronger, and the pass band of the filter becomes wider in the characteristic B than in the characteristic A. The input / output coupling capacitance increases as the passband is widened, but the center frequency is lowered.

As described above, according to this embodiment, the ratio band of the two-stage filter can be controlled by changing the length of the open-end stub which is a discontinuous portion, and the small-size and external environment can be controlled. A filter having stable characteristics can be realized.

[0064]

As described above, according to the present invention, since two stages of filters can be constituted by one resonator, a filter smaller than a conventional filter can be realized. In addition, since the inter-stage coupling is realized by the discontinuous portion provided in the ring resonator, a filter having stable characteristics with respect to the external environment can be realized.

[Brief description of the drawings]

FIG. 1 is a plan view of a dual mode filter according to a first embodiment of the present invention.

FIG. 2 is another plan view of the dual mode filter according to the first embodiment of the present invention.

FIG. 3 is a plan view of a dual mode filter according to a second embodiment of the present invention.

FIG. 4 is a plan view of a dual mode filter according to a third embodiment of the present invention.

FIG. 5 is a perspective view of a dual mode filter according to a fourth embodiment of the present invention.

FIG. 6 is a plan view of a dual mode filter according to a fifth embodiment of the present invention.

FIG. 7 is another plan view of the dual mode filter according to the fifth embodiment of the present invention.

FIG. 8 is a plan view of a dual mode filter according to a sixth embodiment of the present invention.

FIG. 9 is another plan view of the dual mode filter according to the sixth embodiment of the present invention.

FIG. 10 is a plan view of a dual mode filter according to a seventh embodiment of the present invention.

FIG. 11 is a plan view of a dual mode filter according to an eighth embodiment of the present invention.

FIG. 12 is a plan view of a dual mode filter according to the first embodiment of the present invention.

FIG. 13 is a characteristic diagram of a dual mode filter according to the first embodiment of the present invention.

FIG. 14 is a plan view of a conventional side-coupled high-frequency filter.

[Explanation of symbols]

Reference Signs List 101 ring resonator 102 to 103 input / output coupling circuit 104 stub and notch serving as discontinuous part 105 to 106 coupling point of input / output coupling circuit to ring resonator 107 symmetry point 108 discontinuous part line 109 dielectric substrate 110 parallel coupling Line portion 111 Lumped constant inductor 111A Parallel coupling line 112-115 Open end stub 116-118 Interstage coupling circuit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-241201 (JP, A) JP-A-1-289301 (JP, A) JP-A-7-249901 (JP, A) JP-A-5-205 315805 (JP, A) JP-A-63-62405 (JP, A) JP-A-58-99002 (JP, A) JP-A-4-72705 (JP, U) Munenori Fujimura, Hiroyuki Yabuki, Mitsuo Makimoto, Excitation of orthogonal resonance mode of wavelength ring resonator and its application, IEICE technical report MW92-115 (58) Fields investigated (Int. Cl. ⁷ , DB name) H01P 1/20-1/219 H01P 7/00-7/10

Claims (5)

(57) [Claims] A ring resonator formed by connecting a high-frequency transmission line in a ring shape; first and second input / output coupling circuits connecting the ring resonator to an external circuit; A discontinuous portion for generating a field discontinuity, wherein the first input / output coupling circuit is connected to a first coupling point provided at an arbitrary position on the ring resonator;
Is connected to a second coupling point provided at a position separated from the first coupling point by a quarter of the length of the ring resonator, and is connected to the first and second coupling points. Wherein the discontinuous portion is provided around a first point of symmetry separated by one-eighth of the length of the ring resonator, and the discontinuous portion defines a part of a line forming the ring resonator. A dual mode filter, comprising: a parallel coupling line section which is bent 180 degrees at a first symmetry point and parallel coupled. 2. The parallel coupling line portion is formed by a line having a length equal to or more than ４ of the ring resonator, and the parallel coupling line portion is separated from the first symmetry point by ８ of the ring resonator length. The dual mode filter according to claim 1, wherein the first and second coupling points are provided in a coupling line section. 3. A folding the line inside the ring resonator claims, characterized in that the formation of the parallel coupling line sections
2. The dual mode filter according to 1 . 4. A ring resonator formed by connecting a high-frequency transmission line in a ring shape, first and second input / output coupling circuits connecting the ring resonator to an external circuit, A discontinuous portion for generating a field discontinuity, wherein the first input / output coupling circuit is connected to a first coupling point provided at an arbitrary position on the ring resonator;
Is connected to a second connection point provided at a position separated from the first connection point by a quarter of the length of the ring resonator, and is connected to the first and second connection points. The discontinuous portion is provided around a first symmetry point separated by 1/8 of the length of the ring resonator from the first and second coupling points, and A dual mode filter comprising a lumped-constant capacitor connected between two arbitrary points separated by the same length toward one symmetry point. 5. The dual mode filter according to claim 4, wherein the lumped constant capacitance is replaced with a lumped constant inductor.